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As power electronic based controllers and loads become more prevalent in power systems, there is a growing concern about how the harmonics generated by these controllers and loads affect the power quality of the system. One widely used power electronic based load is the Variable Frequency Drive (VFDs) used to vary the speed of an induction motor; whereas a common example of a power electronic based controller used in power systems is the Static VAR Compensator (SVC) for improving a system’s power factor. In this thesis, the harmonic content and overall performance of a system including both a VFD and a SVC will be studied and analyzed. Specifically, the cases of no compensation, static capacitor compensation, and power electronic based static VAR compensation are examined. A small-scale model of a system for study was constructed in lab. Several cases were then performed and tested to simulate a system which contained both fixed and power electronic based harmonic generating loads. The performance of each case was determined by total harmonic current and voltage distortions, true power factor, and RMS current levels at different points in the system.

The benefits of microwave technology in materials processing is well documented and researched. It offers many potential advantages over conventional processing such as rapid heating, faster processing times and more consistent product quality. However the actual implementation of this technology has been lacking and the benefits have gone largely unrealised. This is due largely in part to the non-uniform heating obtained in multimode cavities in conventional microwave processing. Recently, a new processing method dubbed the Variable Frequency Microwave (VFM) Technique has been developed to overcome the inherent problems associated with conventional microwave processing. By sweeping through a bandwidth of frequencies, the limitations observed in conventional processing, and specifically the problem of heat uniformity, are avoided. With the increase in research activities in alternative processing methods for new and current materials that will provide better product quality as well as time and cost savings, the VFM technique has the potential to rejuvenate interest in microwave processing. This thesis documents the research work undertaken on the VFM technique with emphasis on its characterization, optimisation and implementation to suitable applications in particular in the upcoming area of Microfabrication. A commercial Variable Frequency Microwave with an operating bandwidth of 2.5-8.0 GHz was investigated through modelling and experimental work to determine the energy distribution within a multimode cavity and to provide an insight of the mechanisms of the method. Modelling was found to be an efficient and cost-effective tool to simulate VFM and to examine the reported advantages of this new technique. Results obtained confirm the superiority of the VFM method over the conventional fixed-frequency processing showing a marked improvement in the heating uniformity achieved. Quantitative analysis of the three major VFM parameters that influence heat uniformity - Sweep Rate, Bandwidth and Central Frequency - indicate that although slight variation in heat uniformity was observed when changing these parameters, these variations are only small which implies that the VFM technique is quite insensitive to changes in the parameters making it quite a robust system. An analytical model of the Variable Frequency Microwave technique was developed and it was found that the heating uniformity could be further optimised using a sweep rate that varies as the inverse of the frequency squared (weighted-sweep). In this study, VFM Technique was successfully extended to the Micro-Electro- Mechanical Systems (MEMS) industry as an alternative method for the processing of a polymer system - negative-tone SU8 photoresist - which is gaining widespread use in Microfabrication. The VFM method was compared to conventional hotplate curing as well as a new hybrid curing method introduced in this work and the product quality assessed optically and by thermal analysis. Results from this work indicate that the Variable Frequency Microwave technique is a viable alternative to the conventional cure currently used in practice. With proper optimisation of the VFM parameters, VFM was found to provide samples that are comparable or better than conventionally cured samples in terms of properties and microstructure quality. Using the VFM method, enhancement in cure rates and drying rates, which are described by others as microwave effects, were observed and investigated. A significant increase on the degree of cure of up to 20% greater than conventional cure was observed when VFM was utilized and an apparent enhancement in solvent evaporation in the thin SU8 films observed. Experiments undertaken show that microwaves irradiation can enhance diffusion rates of cyclopentanone in the SU8 system by approximately 75-100%. The findings signify that SU8 curing at lower temperatures or rapid curing are possible and long drying times could be reduced significantly thus alleviating many of the problems associated with conventional thermal curing. Outcomes of this study demonstrate the ability of the new VFM technique to provide uniform heating which is essential for materials processing. Its application to the emerging field of Microfabrication exhibits its unique advantages over conventional curing methods and establishes itself to be a versatile and robust processing tool. The experimental observations made under microwave irradiation are further proof of the existence of specific microwave effects which is one of the most debatable topics in the Microwave processing field. A mechanism based on the Cage Model by Zwanzig [1983] was put forward to explain the increase in transport rates.

The presence of partial discharges (PD) in high voltage components is generally a sign of defects and degradation in the electrical insulation. To diagnose the condition of high voltage insulation, PD measurements is commonly used. The Variable Frequency Phase Resolved PD Analysis (VF-PRPDA) technique measures PD at variable frequency of the applied voltage. With this technique, the frequency dependence of PD can be utilized to extract more information about the insulation defects than is possible from traditional PD measurements at a single applied frequency. In this thesis the PD process in a disc-shaped cavity is measured and modelled at variable frequency (0.01 - 100 Hz) of the applied voltage. The aim is to interpret the PD frequency dependence in terms of physical conditions at the cavity. The measurements show that the PD process in the cavity is frequency dependent. The PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, change with the varying frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the size of the cavity and the location of the cavity (insulated or electrode bounded). A physical model is presented and used to dynamically simulate the sequence of PDs in the cavity at different applied frequencies. The simulations show that essential features in the measured PD patterns can be reproduced. The PD frequency dependence is interpreted as a variation in influence on the PD activity from the statistical time lag of PD and the charge transport in the cavity surface, at different applied frequencies. The simulation results also show that certain cavity parameters, like the cavity surface conductivity and the rate of electron emission from the cavity surface, change with the time between consecutive PDs, and accordingly with the applied frequency. This effect also contributes to the PD frequency dependence. / QC 20100722

As the world moves towards eliminating lead from consumer products, the microelectronics industry has put effort into developing lead-free solder paste. The major drawback of lead-free solder is the problems caused by its high reflow temperature. Variable frequency microwave (VFM) processing has been shown to allow some materials to be processed at lower temperatures. Issues addressed in this study include using VFM to reduce the solder reflow temperature, comparing the heating rate of different size solder particles, and comparing the reliability of VFM reflowed solder versus conventionally reflowed solder. Results comparing the effect of particle size on the heating rate of solder showed that the differences were negligible. This is due in part to the particle sizes overlapping. Many lead-free solder pastes reflow around 250℃. Results indicate that when using the VFM, lead-free solder paste will reflow at 220℃. The reliability of solder that was reflowed using the VFM at the reduced temperature was found to be comparable to solder reflowed in a conventional manner. Based on these findings, VFM processing can eliminate the major obstacles to making lead-free solder paste a more attractive option for use in the microelectronics industry.

Induction motors and Variable Frequency Drives (VFDs) are widely used in industry to drive machinery trains. However, some mechanical trains driven by VFD-motor systems have encountered torsional vibration problems. This vibration can induce large stresses on shafts and couplings, and reduce the lifetime of these mechanical parts. Long before the designed lifetime, the mechanical train may encounter failure. This thesis focuses on VFDs with voltage source rectifiers for squirrel-cage induction motors of open-loop Volts/Hertz and closed-loop Field Oriented Control (FOC). First, the torsional vibration problems induced by VFDs are introduced. Then, the mathematical model for a squirrel-cage induction motor is given. Two common control methods used in VFD are discussed - open-loop Volts/Hertz and closed-loop FOC. SimPowerSystems and SimMechanics are used as the modeling software for electrical systems and mechanical systems respectively. Based on the models and software, two interface methods are provided for modeling the coupled system. A simple system is tested to verify the interface methods. The study of open-loop Volts/Hertz control method is performed. The closed-form of electromagnetic torque sideband frequency due to Pulse Width Modulation is given. A torsional resonance case is illustrated. The effects of non-ideal power switches are studied, which shows little in uence on the system response but which uses little energy consumption. A study of a non-ideal DC bus indicates that a DC bus voltage ripple can also induce a big torsional vibration. Next, the study of the closed-loop FOC control method is presented. Simulation for a complete VFD machinery train is performed. With the recti er and DC bus dynamic braking, the system shows a better performance than the ideal-DC bus case. Lastly, a parametric study of the FOC controller is performed. The effects of primary parameters are discussed. The results indicate that some control parameters (i.e. speed ramps, proportional gain in speed PI controller) are also responsible for the mechanical torsional vibration.

Resumo: Em sistemas de bombeamento, a vazão solicitada à bomba nem sempre é constante, normalmente as bombas operam em rotação constante e para obter a variação da vazão, utilizam-se válvulas de estrangulamento na saída. Outro método utilizado é controlar a velocidade do motor através de inversores de freqüência, pois, a variação da vazão é diretamente proporcional à rotação do motor, proporcionando uma maior facilidade de controle e economia de energia, porém, interferindo na qualidade de energia elétrica. Neste contexto, a finalidade deste trabalho foi a comparação do consumo de energia elétrica para dois tipos de controle de vazão em sistemas de bombeamento: por válvula de estrangulamento ou por inversor de freqüência para dois tipos de motores: padrão e de alto rendimento. Comprovou-se que a simples troca de um motor padrão por um motor de alto rendimento gera uma redução de consumo de energia elétrica entre 32,45% a 33,42%, no caso estudado. A substituição do controle de vazão, da válvula de estrangulamento para o controle pelo inversor de freqüência trouxe uma economia de energia elétrica entre 47,18% a 52,22% em determinadas faixas. A substituição do controle de vazão pela válvula e motor padrão para o controle de vazão pelo inversor e motor de alto rendimento gerou uma economia de 67,03%. Para avaliar a influência dos programas de eficiência energética na qualidade da energia foram mensurados valores do fator de potência e dos níveis de distorção harmônica total de corrente e de tensão gerados através de três tipos de acionamento do motor trifásico: partida direta, partida suave e partida com inversor de freqüência, comparando-os com valores da norma brasileira (ANEEL) e de norma internacional (IEC). / Abstract: In pumping systems the flow requested of the pump is not always constant, normally the pumps operate in constant rotation and bottleneck valves are used in order to obtain the flow variation. Controlling the motor speed through variable frequency drives is another used method since the flow variation is directly proporcional to the motor rotation. In this report it was carried out a comparisson of electric power consumption in a pumping system with the flow control by bottleneck valve and by variable frequency drives in order to identify an economically viable range of use. The technical and economical viability of substituting a standard motor for a highperformance motor one was also analysed. It proved that the simple exchange of a standard motor for a high performance one, generates a reduction of electric power consumption between 32.45% a 33.42%, in the studied case. The replacement of the flow control of the bottleneck valve to the variable frequency drives brought a saving of electric power between 47.18% a 52.22% in certain ranges. The replacement of the flow control by the valve and standard motor for the variable frequency drives and the high performance motor generated an economy of 67.03%. It was mensuremented values of power factor and total harmonic distortion of current and voltage generated by three diferent types of starts: direct start, soft-start and variable speed drives start and compared with values of the Brazilian norm (ANEEL) and International norm (IEC) to appraise its influency in energy efficiency programs. / Orientador: Teófilo Miguel de Souza / Coorientador: Pedro Magalhães Sobrinho / Banca: Rubens Alves Dias / Banca: Jamil Haddad / Mestre

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-07Bitstream added on 2014-06-13T20:20:27Z : No. of bitstreams: 1 mesquita_rp_me_guara.pdf: 1170750 bytes, checksum: fa765b6e1b242ea2391a24aa47efeb14 (MD5) / Eletrobras / Em sistemas de bombeamento, a vazão solicitada à bomba nem sempre é constante, normalmente as bombas operam em rotação constante e para obter a variação da vazão, utilizam-se válvulas de estrangulamento na saída. Outro método utilizado é controlar a velocidade do motor através de inversores de freqüência, pois, a variação da vazão é diretamente proporcional à rotação do motor, proporcionando uma maior facilidade de controle e economia de energia, porém, interferindo na qualidade de energia elétrica. Neste contexto, a finalidade deste trabalho foi a comparação do consumo de energia elétrica para dois tipos de controle de vazão em sistemas de bombeamento: por válvula de estrangulamento ou por inversor de freqüência para dois tipos de motores: padrão e de alto rendimento. Comprovou-se que a simples troca de um motor padrão por um motor de alto rendimento gera uma redução de consumo de energia elétrica entre 32,45% a 33,42%, no caso estudado. A substituição do controle de vazão, da válvula de estrangulamento para o controle pelo inversor de freqüência trouxe uma economia de energia elétrica entre 47,18% a 52,22% em determinadas faixas. A substituição do controle de vazão pela válvula e motor padrão para o controle de vazão pelo inversor e motor de alto rendimento gerou uma economia de 67,03%. Para avaliar a influência dos programas de eficiência energética na qualidade da energia foram mensurados valores do fator de potência e dos níveis de distorção harmônica total de corrente e de tensão gerados através de três tipos de acionamento do motor trifásico: partida direta, partida suave e partida com inversor de freqüência, comparando-os com valores da norma brasileira (ANEEL) e de norma internacional (IEC). / In pumping systems the flow requested of the pump is not always constant, normally the pumps operate in constant rotation and bottleneck valves are used in order to obtain the flow variation. Controlling the motor speed through variable frequency drives is another used method since the flow variation is directly proporcional to the motor rotation. In this report it was carried out a comparisson of electric power consumption in a pumping system with the flow control by bottleneck valve and by variable frequency drives in order to identify an economically viable range of use. The technical and economical viability of substituting a standard motor for a highperformance motor one was also analysed. It proved that the simple exchange of a standard motor for a high performance one, generates a reduction of electric power consumption between 32.45% a 33.42%, in the studied case. The replacement of the flow control of the bottleneck valve to the variable frequency drives brought a saving of electric power between 47.18% a 52.22% in certain ranges. The replacement of the flow control by the valve and standard motor for the variable frequency drives and the high performance motor generated an economy of 67.03%. It was mensuremented values of power factor and total harmonic distortion of current and voltage generated by three diferent types of starts: direct start, soft-start and variable speed drives start and compared with values of the Brazilian norm (ANEEL) and International norm (IEC) to appraise its influency in energy efficiency programs.

No description available.

[pt] Uma bomba centrífuga, depois de concluída a sua instalação, deve vencer uma elevação constante. A variação da rotação vai alterar diretamente a descarga. Como bomba centrífuga é acionada por motor de indução, a variação da freqüência não acarreta variação proporcional na rotação devido a que a nova rotação implica em outro valor da descarga que somente ocorre com torque diferente do anterior e em conseqüência, o deslizamento deve se ajustar para igualar o torque fornecido pelo motor com o novo torque requerido pela bomba. A análise parte dos estudos que relacionam a descarga com a rotação para relacionar a descarga com a freqüência. / [en] Once installation is concluded, a centrifugal pump should withstand constant head. The variation of rotation directly alters the discharge. Since centrifugal pump operates by induction motor, the variation in frequency does not lead to proporcional variation in rotation due to the new rotation being of another discharge value which only occurs with a different torque. Consequently, the sllep should adjust itself to equalize the torque provided by the motor to the new torque required by the pump. The analisis derives from studies which related the discharge to the rotation in order to relate the discharge to the frequency.